Capacitance-type occupant detection sensor

ABSTRACT

A capacitance-type occupant detection sensor of the present disclosure detects a vehicle occupant on a seat based on a difference of capacitance between a sensor body and a reference electric potential. The sensor body includes a main electrode and a parallel electrode. The parallel electrode is disposed in parallel with the main electrode with a gap interposed therebetween and has a detection voltage applied thereto. The main electrode and the parallel electrode each have a base material, a first electrode member disposed on the base material, and a second electrode member disposed on the base material to cover the first electrode member, where the second electrode member has an electric conductivity that is lower than the first electrode member. The first electrode member is disposed on a lateral perimeter of the second electrode member to surround a center of the second electrode member.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority ofJapanese Patent Application No. 2012-130147 filed on Jun. 7, 2012, thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to a capacitance-type occupantdetection sensor used in an automobile.

BACKGROUND

A capacitance-type occupant detection sensor detects an occupant seatedon a seat of the vehicle by detecting a change of capacitance betweentwo electrodes. In order to reduce production cost, in some cases thecapacitance-type occupant detection sensor is designed to have itselectrodes made of two kinds of materials. For example, Japanese PatentLaid-Open No. 2008-111809 (i.e., patent document 1) discloses a sensorthat has silver electrodes made of silver and carbon electrodes made ofcarbon. The price of the carbon is lower than that of the silver,thereby enabling the reduction of the production cost.

However, in terms of electric conductivity the carbon is lower than thesilver. Therefore, due to a greater electric resistance in the carbonelectrode, the electric voltage of the carbon electrode that covers thesilver electrode is lower than the applied voltage at a portion of thecarbon electrode that is far from the silver electrode, or at anedge/periphery portion of the carbon electrode.

When the same voltage is applied to adjacent electrodes, an electricfield may be formed between the two adjacent electrodes, since aperiphery voltage of the electrode may be lower than the appliedvoltage. Therefore, the accuracy of the detected electric current maydeteriorate, thereby leading to deterioration in accuracy of thedetected capacitance as well as to the occupant detection.

SUMMARY

In an aspect of the present disclosure, a capacitance-type occupantdetection sensor detects a vehicle occupant on a seat of a vehicle basedon a capacitance value between a reference voltage and a sensor body.The sensor body is disposed in the seat, and includes a main electrodeand parallel electrode.

The main electrode and the parallel electrode have a detection voltageapplied thereto. The parallel electrode is disposed in parallel with themain electrode with a gap interposed therebetween.

The main electrode and the parallel electrode each have a base material,a first electrode member disposed on the base material, and a secondelectrode member disposed on the base material to cover the firstelectrode member. The first electrode member is disposed on a lateralperimeter of the second electrode member to surround a center of thesecond electrode member. The second electrode member has an electricconductivity that is lower than the first electrode member.

In such a configuration, since the main electrode and the parallelelectrode have the first electrode member, which has a high electricconductivity, disposed along its lateral perimeter, the voltage at theperiphery of the main electrode and the parallel electrode does notdecrease, thereby reducing the unwanted capacitance coupling between themain electrode and the parallel electrode. In other words, at a time ofdetecting an occupant, the formation of the electric field between theelectrodes inside of the sensor body is prevented. Therefore, thecapacitance detection accuracy is improved, and, as a result, theoccupant detection accuracy is also improved.

In another aspect, the sensor body includes a main electrode, a parallelelectrode, and a guard electrode. The main electrode and the parallelelectrode have the detection voltage applied thereto, and the guardelectrode has the same voltage applied thereto as the detection voltage.

The main electrode has a loop portion and a non-loop portion. The loopportion has a terminating end connected to the main electrode, and thenon-loop portion extends from the loop portion.

The parallel electrode is disposed in parallel with the main electrodewith a gap interposed therebetween. The parallel electrode is disposedalong a first lateral side of the loop portion, and has a starting endand a terminating end positioned on both sides of the non-loop portion.

The guard electrode is arranged to face the main electrode, and has afacing part and a protrusion part. The facing part faces the mainelectrode and the protrusion part extends from the facing part in adirection away from the parallel electrode, such that the protrusionpart extends towards a second lateral side of the loop portion, which isopposite of the first lateral side of the loop portion.

In recent years, a structure having the parallel electrode on bothlateral sides (i.e., sides relative to the width) of the main electrodeis used for preventing the unwanted capacitance coupling. However, theinventors of the present disclosure found that such structure restrictsthe shape of the main electrode due to the arrangement of the parallelelectrode on both sides of the main electrode. In other words, if themain electrode is configured to have a loop shape, the parallelelectrode divided into two parts, i.e., the inner circumference side andthe outer circumference side, has to have a complicated structure inorder to connect with each other, which may increase the productioncost.

On the other hand, if the main electrode is not configured to have theloop shape, the resistance of the main electrode is not reduced, andsuch resistance in the main electrode leads to the electric potentialdifference, thereby causing an inaccuracy of the electric currentmeasurement and resulting in the deteriorated accuracy of thecapacitance detection and the occupant detection. Therefore, looping ofthe main electrode without complicating the electrode structure isdesired to reduce the influence between the electrodes in the sensorbody and avoiding the unwanted capacitance coupling in order to improvethe accuracy of the capacitance-type occupant detection sensor at lowcost.

The present disclosure enables the reduction of the unwanted capacitancecoupling on both sides of the main electrode by providing (i) theparallel electrode on one lateral side (i.e., first lateral side) of themain electrode, and (ii) the protrusion part of the guard electrode onthe other lateral side (i.e., a second lateral side) of the mainelectrode. Further, the parallel electrode is positioned only on oneside of the main electrode, which enables the parallel electrode to bearranged in parallel and along the main electrode without complicatingthe structure, i.e., without splitting the parallel electrode into twoparts or the like. Therefore, the inter-electrodes influence in thesensor body is prevented at a low cost, and the capacitance detectionaccuracy and the occupant detection accuracy is also improved.

In yet another aspect of the present disclosure, a capacitance-typeoccupant detection sensor includes a sensor body and a detection part.The sensor body is disposed in the seat of the vehicle and includes amain electrode, a parallel electrode, and a guard electrode. The mainelectrode and the parallel electrode have the detection voltage appliedthereto, and the guard electrode has the same voltage applied thereto asthe detection voltage.

The parallel electrode is disposed in parallel with the main electrodewith a gap interposed therebetween. The guard electrode has a facingpart and a sub-guard part. The facing part is arranged to face the mainelectrode, and the sub-guard part is disposed between the main electrodeand the parallel electrode. The facing part and the sub-guard part havethe same voltage applied thereto as the detection voltage.

The detection part detects an occupant on the seat based on acapacitance value between the main electrode and a reference electrode.The detection part also detects a liquid spill on the seat based on acapacitance between the main electrode and the parallel electrode when apredetermined voltage is applied to the parallel electrode.

Around the main electrode, the parallel electrode is arranged so thatthe main and parallel electrodes run in parallel with a gap. By havingthe same electric potential applied to both of the main and parallelelectrodes, the unwanted capacity coupling with a surrounding object bythe main electrode is prevented or at least reduced.

Further, the parallel electrode, which has the predetermined electricpotential, forms an electric field together with the main electrode,which has the detection voltage applied thereto. The parallel electrodeserves as an electrode for detecting the liquid spill based on thecapacitance between the main and parallel electrodes. In such manner,the parallel electrode functions as a guard electrode for guarding theperiphery of the main electrode and also functions as a spill electrodefor detecting the liquid spill.

When the parallel electrode is used as the guard electrode, the guardperformance is higher when the parallel electrode is positioned closerto the main electrode. In other words, the occupant detection accuracyis improved when the parallel electrode is closer to the main electrode.

On the other hand, when the parallel electrode is used as the spillelectrode, the capacitance change at the liquid spill time is greater,i.e., the sensitivity is improved, when the distance between the mainelectrode and the parallel electrode is larger to some extent. In otherwords, the liquid spill detection accuracy is improved when the distanceis greater to some extent.

Therefore, improvement of both of the occupant detection accuracy andthe water spill detection accuracy is desired.

In yet another aspect of the present disclosure, the main electrode andthe parallel electrode are interposed with the sub-guard part of theguard electrode. In such a structure, the sub-guard part has the sameelectric potential as the guard electrode to be serving as the guardelectrode.

In such a structure, the distance between the main electrode and thesub-guard part is enabled to be small, because of the arrangement of thesub-guard part between the main and parallel electrode. That is, theunwanted capacity coupling with the surrounding object is prevented orreduced for the improvement of the occupant detection accuracy.

Further, in such a structure, the distance between the main electrodeand the parallel electrode is enabled to be large, because of thearrangement of the sub-guard part. Therefore, the sensitivity for theliquid spill is improved, thereby improving the liquid spill detectionaccuracy.

The present disclosure having the above structure enables theimprovement of both of the occupant detection accuracy and the liquidspill detection accuracy without compromise, based on the prevention ofthe unwanted capacitance coupling with the surrounding object.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present disclosure willbecome more apparent from the following detailed description disposedwith reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a capacitance-type occupant detectionsensor in a first embodiment of the present disclosure;

FIG. 2 is a circuit diagram of the capacitance-type occupant detectionsensor of the first embodiment;

FIG. 3 is a top view of a sensor body of the first embodiment;

FIG. 4 is a cross-sectional view of the sensor body along line IV-IV ofFIG. 3;

FIG. 5 is a diagram of an electric voltage of a main electrode and asub-electrode along of the sensor body of the first embodiment;

FIG. 6 is an illustration of an electric line of force formed on themain electrode and the sub-electrode of the sensor body of the firstembodiment;

FIG. 7 is a graphical illustration of a comparison example of acapacitance difference generated by a conventional technique versus thesensor body of the first embodiment;

FIG. 8 is a graphical illustration of a change of capacitance of thesensor body of the first embodiment caused by an external factor;

FIG. 9 is a capacitance-type occupant detection sensor of a conventionaltechnique;

FIG. 10 is a circuit diagram of a capacitance-type occupant detectionsensor in a second embodiment of the present disclosure;

FIG. 11A is a top view of a sensor body of the second embodiment;

FIG. 11B is an exploded view of the sensor body about XIB of FIG. 11A;

FIG. 12 is a cross-sectional view of the sensor body along line XII-XIIof FIG. 11A;

FIG. 13 is a graphical illustration of a resistance value of the mainelectrode of the sensor body of the second embodiment;

FIG. 14 is a graphical illustration of a comparison example of acapacitance difference generated by a conventional technique versus thesensor body of the second embodiment;

FIG. 15 is a top view of the sensor body illustrating a non-loop portionof the main electrode being positioned inside of a loop portion of themain electrode of the sensor body of the second embodiment;

FIG. 16 top view of the sensor body illustrating a non-loop portion ofthe main electrode being positioned outside of a loop portion of themain electrode of the sensor body of the second embodiment;

FIG. 17 is a circuit diagram of a capacitance-type occupant detectionsensor in a third embodiment of the present disclosure;

FIG. 18 is a top view of the sensor body of the third embodiment;

FIG. 19 is a cross-sectional view of the sensor body along line XIX-XIXof FIG. 18;

FIG. 20 is a graphical illustration of a comparison example of a dry-wetdifference of impedance values generated by a conventional techniqueversus the sensor body of the third embodiment; and

FIG. 21 is a circuit diagram of the capacitance-type occupant detectionsensor in a modification of the third embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure is described in the following with reference tothe drawings.

<First Embodiment>

With reference to FIG. 1, the capacitance-type occupant detection sensorin the first embodiment includes a sensor body 1 and an occupantdetection ECU 2. The sensor body 1 is a film-shaped sensor mat, in whichthe electrode has a zigzag shape. The sensor body 1 is disposed in aseat 91 of the vehicle. The sensor body 1 is disposed substantially inparallel with a seat surface 911 of the seat 91.

With reference to FIGS. 2-4, the sensor body 1 includes a main electrode11, a sub-electrode 12, a guard electrode 13, and film members 14, 15,16. The main electrode 11 is a flatboard-shaped conductive member, andis disposed on the film member 15. The film member may be provided as abase material.

The sub-electrode 12 is a flat board-shaped conductive member, and isdisposed on both sides of the main electrode 11, so that the mainelectrode 11 and the sub-electrodes 12 are arranged next to each otheron the film member 15. In other words, the sub-electrodes 12 arearranged in parallel with the main electrode 11 with a gap interposedbetween the sub-electrode 12 and a periphery of the main electrode 11.The sub-electrode 12 is arranged along the periphery of the mainelectrode 11. The main electrode 11 and the sub-electrode 12 arearranged between the film member 14 and the film member 15. Thesub-electrode 12 may be referred to as a parallel electrode.

The guard electrode 13 is a flat board-shaped conductive member, and isdisposed to face the main electrode 11 with the film member 15interposed between the main electrode 11 and the guard electrode 13. Afilm member 16 is disposed on a lower side of the guard electrode 13. Inother words, the guard electrode 13 is arranged between the film member15 and the film member 16.

The film members 14, 15, 16 are made of non-conductive material, such aspolyethylene terephthalate (PET), and the film members 14, 15, 16 havean adhesive solution interposed therebetween.

The occupant detection ECU 2 is an electronic control unit, and includesa voltage application part 21, a current detecting part 22, acapacitance detecting part 23, a distinction part 24, and an op-amp 25.

The voltage application part 21 is connected to a vehicle ground GND andto the main electrode 11. The voltage application part 21 is an AC powersupply, and applies an alternate voltage (i.e., a detection voltage) tothe main electrode 11. In such manner, the main electrode 11 forms anelectric field with a vehicle body 3.

The current detecting part 22 is a current sensor, and detects anelectric current flowing in the main electrode 11. The electric currentis caused by an application of an electric voltage by the voltageapplication part 21. The capacitance detecting part 23 is connected tothe current detecting part 22 and to the distinction part 24. Thecapacitance detecting part 23 calculates capacitance in the electricfield that is formed by the main electrode 11 based on the electricvoltage applied by the voltage application part 21 and the electriccurrent detected by the current detecting part 22. The capacitance iscalculable based on an imaginary part of an impedance of an electriccurrent path at a time of application of the electric voltage, and theimaginary part is calculable from a phase gap between a phase of theelectric current and a phase of the electric voltage.

The distinction part 24 distinguishes, or detects, whether there is anoccupant on the seat 91 and whether the occupant is an adult or a childin a child restraint system (CRS) based on a detection result of thecapacitance detecting part 23 and a predetermined threshold set inadvance.

The op-amp 25 has, on an input side, the voltage application part 21connected thereto and has, on an output side, the sub-electrode 12 andthe guard electrode 13 connected thereto. The op-amp 25 applies, tosub-electrode 12 and the guard electrode 13, an electric voltage that issame as the voltage applied to the main electrode 11. Therefore, themain electrode 11, the sub-electrode 12, and the guard electrode 13 havethe same electric potential when the capacitance-type occupant detectionsensor is in an occupant detection mode.

The guard electrode 13 prevents a formation of the electric field thatis formed by the main electrode 11 and the vehicle body 3 by having thesame electric potential as the main electrode 11 on the lower side ofthe main electrode 11. That is, a formation of the electric fieldotherwise formed between the main electrode 11 and the vehicle body 3 isprevented by the guard electrode 13, thereby guaranteeing a formation ofthe electric field by the main electrode 11 only on an upper side of themain electrode 11, i.e., on or above the seat 91 or the seat surface911.

The sub-electrode 12 is an electrode that prevents an electric line offorce to extend from a side portion (i.e., the periphery) of the mainelectrode to the vehicle body 3 without passing through the seat 91 andthe occupant. That is, the sub-electrode 12 prevents a formation of theelectric field between the main-electrode 11 and the vehicle body 3,thereby controlling the electric line of force from the main electrode11 in a horizontal direction.

Therefore, the sub-electrode 12, which has the same electric potentialas the main electrode 11, enables a formation of the electric field bythe main electrode 11 and the vehicle body 3 in a space above the seat91, with the electric line of force passing through the seat 91.

The sub-electrode 12 may also be used as an electrode to detect a liquidspill, such as a water spill, on the seat 91. When the sensor is in theliquid spill detection mode, the reference electric potential (i.e., thevehicle GND) is applied to the sub-electrode 12, and an electric fieldis formed between the main electrode 11, which has the detection voltageapplied thereto, and the sub-electrode 12 having the reference electricpotential. Based on a capacitance between the relevant electrodes, theliquid spill is detected.

The vehicle body 3 serves as an electrode in addition to be serving as abody of the vehicle, and the vehicle body 3 has the reference electricpotential, which is also designated as ground GND.

In FIG. 4 provides a view of the sensor body 1 along a horizontal axis(H-axis), where the width of the main electrode 11, sub-electrode 12,and guard electrode 13 is along the H-axis. The main electrode 11 has asilver part 111 that is made of silver and a carbon part 112 that ismade of carbon. The silver part 111 may have a rectangular orparallelepiped shape that extends in a rod shape, and is disposed in twoparallel lines that extend along an extending direction of the mainelectrode 11 (e.g., extend along a direction to form the pattern of FIG.3). The silver part 111 may be referred to as a first electrode memberin claims.

The carbon part 112 may extend as a flat-board shape disposed to coverthe silver part 111 which forms two lines along the extending directionof the main electrode 11. The carbon part 112 may be referred to assecond electrode member in claims. Since the electric conductivity ofthe carbon is lower than the electric conductivity of the silver, theelectric conductivity of the carbon part 112 is lower than the electricconductivity of the silver part 111.

The silver part 111 is covered by the carbon part 112, and is disposedat a lateral perimeter of the carbon part 112 along the H-axis of themain electrode. In other words, the silver part 11 is positioned at bothlateral sides of the main electrode 11 along the H-axis, and is withinthe carbon part 112. The silver part 111 is disposed to surround acenter part of the carbon part 112, which is a center part of the mainelectrode 11. The silver part 111 and the carbon part 112 have a certainvoltage applied by the voltage application part 21 in order to have acertain electric potential generated thereon.

Similarly, the sub-electrode 12 is structured to have a silver part 121and a carbon part 122. The guard electrode 13 is structured to have asilver part 131 and a carbon part 132. The guard electrode 13 has thesame dimension as the main electrode 11. The sub-electrode 12 extendsparallel with the main electrode 11, and is disposed adjacently on bothsides of the main electrode 11 with a gap interposed therebetween. Thesilver part 121 of the sub-electrode 12 extends in the same direction asthe silver part 111 of the main electrode 11, thereby forming two linesin parallel with each other.

The silver parts 121, 131 are similar to the silver part 111, such thatthe silver parts 121, 131 are covered by the carbon part 122, 132,respectively, and are disposed on a lateral perimeter of the carbon part122, 132. The silver parts 121, 131 are disposed to surround a centerpart of the carbon part 122, 132, respectively. In other words, thesilver parts 121, 131 are disposed to surround a center part of thesub-electrode 12 and the guard electrode 13, respectively.

In the present embodiment, all electrodes 11, 12, 13 are configured tohave the same distance (i.e., “X” in FIG. 6) between an outer edge ofthe carbon part 112, 122, 132 and an outer edge of the silver part 111,121, 131 along the horizontal axis.

According to the configuration of the capacitance-type occupantdetection sensor of the present embodiment, the silver parts 111, 121,which have a relatively high electric conductivity, are disposed alongthe lateral sides of the electrodes 11, 12, respectively. Therefore, asshown in FIG. 5, the electric potential of electrodes 11, 12 issubstantially the same as the applied potential at the periphery, anddoes not have a lower value at the periphery. In particular, “A”, “B”,and “C” of FIG. 5 correspond to the position “A”, “B”, and “C” along thehorizontal axis of FIG. 4.

In such manner, a formation of the electric field between the electrodes11, 12 is prevented, thereby preventing the fluctuation of the electriccurrent value that is detected by the current detecting part 22. Inother words, according to the present embodiment, fluctuation of theelectric current value is reduced or prevented, and the detectionaccuracy of the capacitance and the occupant detection is improved.

According to the present embodiment, as shown in FIG. 6, the unwantedcapacitance coupling caused by the difference of the electric potentialsbetween the electrodes 11, 12, which are adjacent to each other, isreduced. Further, the silver parts 111, 121 are positioned at the samedistance from the outer edge of the electrodes 11, 12, respectively.Therefore, respective peripheries of the electrodes 11, 12 are made tohave the same electric potential. Therefore, the unwanted capacitancecoupling is further reduced.

As shown in FIG. 7, a difference of capacitance (pF) between an adultsitting value and a one-year old child in the CRS sitting value isshown. In particular, the capacitance-type occupant detection of thepresent embodiment produces a greater difference of capacitance thanthat of a conventional technique, such as the conventional techniqueshown in FIG. 9, where the silver electrode is positioned at the centerof the carbon electrode. The capacitance-type occupant detection of thepresent embodiment improves the accuracy of distinctive detection todistinguish between an adult and a child in a CRS.

Further, as shown in FIG. 8, the fluctuation of the detection accuracydue to an external factor, such as natural wear, is reduced by half ormore. The graph in FIG. 8 illustrates a change of capacitance caused byan external factor such as a wear from normal usage, which is measuredby a vertical axis of capacitance (pF). Again, according to the presentembodiment, the detection accuracy for detecting an occupant isimproved.

The present disclosure is not limited to the above embodiment. Forinstance, a modification of the above embodiment may be that the sensorbody 1 does not have the sub-electrode 12 and a “parallelism with a gap”between two peripheries of the main electrode 11 is arrangement eitherby having a slit on the periphery or by forming the electrode 11 in azigzag shape. That is, the two peripheries in parallel may be theperipheries of the same electrode (e.g., the main electrode 11). Such aconfiguration also prevents a capacitance coupling between the mainelectrodes 11 because a center of the electrode is surrounded by thesilver part 111 that is arranged on the periphery of the electrode.

Further, the sub-electrode 12 may be arranged only on one side of themain electrode 11.

Further, in the present disclosure, the water spill may be detected byusing the sub-electrode 12 as described above.

Further, the present disclosure may have a configuration that has theguard electrode 13 omitted therefrom.

Further, the material forming an electrode are not necessarily limitedto the above, as long as the electric conductivity of the material ofthe electrode on the lateral side or lateral perimeter is higher thanthe electric conductivity of the material covering the electrode on thelateral side or later perimeter.

<Second Embodiment>

The capacitance-type occupant detection sensor in the second embodimentis different from the first embodiment mainly in that the sub-electrodeis disposed only on one side of the main electrode, and the guardelectrode has a protrusion part.

With reference to FIG. 10, the capacitance-type occupant detectionsensor in the second embodiment includes a sensor body 4 and an occupantdetection ECU 5. The sensor body 4 corresponds to the sensor body havingthe numeral 1 of FIG. 1.

With reference to FIGS. 11A, 11B, and 12, the sensor body 4 is afilm-shaped sensor mat, in which the electrode has a zigzag shape. Thesensor body 4 is disposed in the seat 91 of the vehicle and issubstantially in parallel with the seat surface 911 of the seat 91. Thesensor body 4 includes a main electrode 41, a sub-electrode 42, a guardelectrode 43, and film members 44, 45 46.

The main electrode 4 is a flat board-shaped conductive member, and isdisposed on the film member 45. The main electrode 41 includes a loopportion 411 starting from and ending at an end part 41 a, and a non-loopportion 412 having a linear shape that extends from the loop portion411. The non-loop portion 412 may be arranged inside (i.e., on an innercircumference side), like shown in FIG. 11A, or outside (i.e., on anouter circumference side) of the loop portion 411, and is connected tothe occupant detection ECU 5.

The sub-electrode 42 is a flat board-shaped conductive member, and isdisposed on the film member 45 next to the main electrode 41, such thatthe sub-electrode 42 is on one side of the main electrode 41. Inparticular, in FIG. 12, which shows the sensor body 1 along the H-axis,the sub-electrode 42 is positioned on one side of the mail electrode 41.When viewed from the top, the sub-electrode 42 extends along the innercircumference side (i.e., extends along a lateral side) of the loopportion 411 of the main electrode 41 (FIGS. 11A, 11B). In other words,the sub-electrode 42 is arranged to be next to and in parallel with theloop portion 411 with a gap interposed therebetween. The sub-electrode42 may be referred to as a parallel electrode in claims.

Along with being disposed on an inside of the loop portion 411, thesub-electrode 42 is arranged on both lateral sides of the non-loopportion 412 as an extension from the inside of the loop portion 411, andis parallel with the non-loop portion 412 with a gap interposedtherebetween. A starting end 42 a and a terminating end 42 b of thesub-electrode 42 are arranged in parallel with an end (i.e., a startingend) of the non-loop portion 412, and are connected to the occupantdetection ECU 5. In other words, the starting end 42 a of thesub-electrode 42 and the terminating end 42 b of the sub-electrode 42are disposed on the inner circumference side of the loop portion 411.

The film member 44 is placed on the main electrode 41 and thesub-electrode 42. In other words, the main electrode 41 and thesub-electrode 42 are arranged between the film member 44 and the filmmember 45.

The guard electrode 43 is a flat board-shaped conductive member, and isdisposed to face the main electrode 41 with the film member 45positioned between the main electrode 41 and the guard electrode 43. Thefilm member 46 is disposed under the guard electrode 43, such that theguard electrode 43 is arranged between the film member 45 and the filmmember 46. The film members 44, 45, 46 are, for example, made ofnon-conductive material (e.g., PET) and have an adhesive solutioninterposed therebetween.

With continuing reference to FIG. 12, the guard electrode 43 has afacing part 431 and a protrusion part 432. The facing part 431 faces themain electrode 41 and is aligned under the main electrode with the filmmember 45 disposed therebetween. The protrusion part 432 extends fromthe facing part 431, such that it protrudes on the other side of mainelectrode 41 (i.e., extends in a direction away from the sub-electrode42 along the H-axis). In particular, when viewed from the top, theprotrusion part 432 extends along the outer circumference side (i.e.,extends along a lateral side) of the loop portion 411 past the peripheryof the main electrode 41, except for the periphery of the correspondingto the non-loop portion 412.

In short, the facing part 431 overlaps with the main electrode 41, andthe protrusion part 432 protrudes from a lateral side, which is oppositeto the side to which the sub-electrode 42 is arranged relative to themain electrode 41, such that the protrusion part 431 does not overlapwith or is not aligned under the main electrode 41. The protrusion part432 is disposed for a part that at least corresponds to the loop portion411, and is not disposed for a part that corresponds to the non-loopportion 412 in the present embodiment.

The occupant detection ECU 5 is an electronic control unit, and includesa voltage application part 51, a current detecting part 52, acapacitance detecting part 53, a distinction part 54, and an op-amp 55.

The voltage application part 51 is connected to a vehicle ground GND andto the main electrode 41. The voltage application part 51 is an AC powersupply, and applies an alternate voltage (i.e., a detection voltage) tothe main electrode 41. In such manner, the main electrode 41 forms anelectric field together with the vehicle body 3.

The current detecting part 52 is a current sensor, and detects anelectric current flowing in the main electrode 41, which is caused by anapplication of an electric voltage by the voltage application part 51.

The capacitance detecting part 53 is connected to the current detectingpart 52 and to the distinction part 54. The capacitance detecting part53 calculates capacitance in the electric field that is formed by themain electrode 41 based on the electric voltage applied by the voltageapplication part 51 and the electric current detected by the currentdetecting part 52.

The capacitance is calculable based on an imaginary part of an impedanceof an electric current path at a time of application of the electricvoltage, and the imaginary part is calculable from a phase gap between aphase of the electric current and a phase of the electric voltage.

The distinction part 54 distinguishes, or detects, whether there is anoccupant on the seat 91, and whether the occupant is an adult or a childin a CRS based on a detection result of the capacitance detecting part53 and a predetermined threshold set in advance.

The op-amp 55 has, on an input side, the voltage application part 51connected thereto and has, on an output side, the sub-electrode 42 andthe guard electrode 43 connected thereto. The op-amp 55 applies, tosub-electrode 42 and the guard electrode 43, a voltage that is the sameas the voltage applied to the main electrode 41. Therefore, the mainelectrode 41, the sub-electrode 42 and the guard electrode 43respectively have the same electric potential when the capacitance-typeoccupant detection sensor is in an occupant detection mode.

By having the same electric potential as the main electrode 41, thefacing part 431 of the guard electrode 43, which is on the lower side ofthe main electrode 41, prevents a formation of the electric field thatis formed by the main electrode 41 and the vehicle body 3. That is, aformation of the electric field by the main electrode 41 in a spaceother than above the seat 91 or at the seat surface 911 is prevented insuch manner. Further, by protruding toward the outer circumference sideand having the same electric potential as the main electrode 41, theprotrusion part 432 prevents a formation of an electric field by themain electrode 41 toward an outer circumference side of the loop portion411 and reduces the unwanted capacitance coupling on the outercircumference side. In other words, the protrusion part 432 plays a rollof the sub-electrode 42.

By having the same electric potential as the main electrode 41 on theinner circumference side of the loop portion 411 and on both sides ofthe non-loop portion 412, the sub-electrode 42 reduces the unwantedcapacitance coupling of the main electrode 41 on an inner circumferenceside of the main electrode 41.

Similar to the first embodiment, the sub-electrode 42 may serve as anelectrode to detect the liquid spill.

According to the configuration of the capacitance-type occupantdetection sensor in the second embodiment, the terminating end 41 a ofthe main electrode 41 is connected to the main electrode 41 itself toform the loop portion 411, because the main electrode 41 (i.e., the loopportion 411) is guarded on one side and on the other side by differentelectrodes. In such manner, the unwanted capacitance coupling on bothsides of the main electrode 41 is reduced, and the resistance of themain electrode 41 is reduced by having a loop shape, thereby improvingthe detection accuracy of the capacitance and the occupant detection.

For instance, with reference to FIG. 13, the resistance value of themain electrode 41 in the present embodiment is reduced by 64% relativeto a conventional configuration that does not have the loop portion 411.

Further, with reference to FIG. 14, in comparison to the conventionaltechnique, the capacitance-type occupant detection sensor of the secondembodiment has a greater difference of capacitance (pF) for an adultsitting value and a one-year old child in a CRS sitting value.

In addition, the structure of the sensor is simplified by having theguard electrode 43 protruding from one side, which serves as asubstitute of the sub-electrode 42 on such side, thereby preventing theincrease of the production cost.

Further, the sub-electrode 42 may be disposed on only one of the innercircumference side or the outer circumference side. In general, thearrangement of the sub-electrode 42 on the inner circumference side ofthe loop portion 411 is illustrated in FIG. 15, and an arrangement ofthe sub-electrode 42 on the outer circumference side of the loop portion411 is illustrated in FIG. 16.

The inner circumference side and the outer circumference side may bereferred to as a first lateral side and a second lateral side,respectively, or as a second lateral side and a first lateral side,respectively.

The present disclosure is not limited to the above-describedembodiments. For example, a modification of the second embodiment may bethat the facing part 431 and the protrusion part 432 of the guardelectrode 43 are partially connected, such that a portion of theprotrusion part 432, which is not connected to the facing part 431, isarranged in parallel with the facing part 431 with a gap interposedtherebetween. In other words, the protrusion part 432 may be disposedalong a periphery of the facing part 431 as a separate part, which maybe partially connected to the facing part 431.

Further, the starting end may be a connecting part in the sensor body 4which is connected to the occupant detection ECU 5.

<Third Embodiment>

The capacitance-type occupant detection sensor in the third embodimentis different from the above embodiments mainly in that a sub-guardelectrode is disposed in between the main electrode and thesub-electrode electrode.

The capacitance-type occupant detection sensor in the third embodimentincludes, as shown in FIG. 17, a sensor body 6 and an occupant detectionECU 7, and the sensor body 6 corresponds to the sensor body having thenumeral 1 in FIG. 1.

The sensor body 6 is a film-shaped sensor mat, in which the electrodehas a zigzag shape. The sensor body 6 is disposed in the seat 91 of thevehicle, and is substantially in parallel with the seat surface 911 ofthe seat 91.

With reference to FIGS. 18-19, the sensor body unit 6 includes a mainelectrode 61, a sub-electrode 62, a guard electrode 63, and film members64, 65, 66. The main electrode 61 is a flat board-shaped conductivemember, and is disposed on the film member 65.

The sub-electrode 62 is a flat board-shaped conductive member, and isdisposed on the film member 65 next to the main electrode 61 and on bothsides of the main electrode 61. In other words, the sub-electrode 62 isarranged to be parallel with the main electrode 61 with a gap interposedtherebetween. The sub-electrode 62 may be referred to as a parallelelectrode in claims.

The film member 64 is disposed on the main electrode 61 and thesub-electrode 62, such that the main electrode 61 and the sub-electrode62 are arranged between the film member 64 and the film member 65.

The guard electrode 63 is a flat board-shaped conductive member, and hasa facing part 631 facing the main electrode 61 and a sub-guard part 632.The film member 66 is disposed under the facing part 631, such that thefacing part 631 is arranged between the film member 65 and the filmmember 66.

The film members 64, 65, 66 may be made of a non-conductive material(e.g., PET), and the film members 64, 65, 66 have an adhesive solutioninterposed therebetween.

The sub-guard electrode part 632 is electrically coupled to the facingpart 631, and is disposed in between the main electrode 61 and thesub-electrode 62 along the periphery of the main electrode 61. In otherwords, the sub-guard part 632 is disposed on both sides of the mainelectrode 61, is arranged to be parallel with the main electrode 61, andhas a gap interposed therebetween. The sub-guard electrode part 632 hasThe same electric potential as the facing part 631.

The sub-guard part 632 is disposed between the film member 64 and thefilm member 65. The sub-guard part 632 and the facing part 631 areelectrically connected via a channel 65A, which is formed on the filmmember 65.

With reference to FIG. 21, the occupant detection ECU 7 is an electroniccontrol unit, and includes a voltage application part 71, a currentdetecting part 72, a capacitance detecting part 73, a distinction part74, an op-amp 75, and a switch part 76. The occupant detection ECU 7 maybe referred to as a detecting unit in claims.

The voltage application part 71 is connected to the vehicle ground GNDand to the main electrode 61. The voltage application part 71 is an ACpower supply, and applies an alternate voltage (i.e., a detectionvoltage) to the main electrode 61. In such manner, the main electrode 61forms an electric field together with the vehicle body 3.

The current detecting part 72 is a current sensor, and detects anelectric current flowing in the main electrode 61, which is caused by anapplication of an electric voltage by the voltage application part 71.

The capacity detecting part 73 is connected to the current detectingpart 72 and the distinction part 74. The capacitance detecting part 73calculates capacitance in the electric field that is formed by the mainelectrode 61 based on the electric voltage applied by the voltageapplication part 71 and the electric current detected by the currentdetecting part 72.

The capacitance is calculable based on an imaginary part of an impedanceof an electric current path at a time of application of the electricvoltage, and the imaginary part is calculable from a phase gap between aphase of the electric current and a phase of the electric voltage.

In an occupant detection mode, the distinction part 74 distinguishes, ordetects, whether there is an occupant on the seat 91 and whether theoccupant is an adult or a child in a CRS based on a detection result ofthe capacitance detecting part 73 and a predetermined threshold set inadvance.

In a spill detection mode, the distinction part 74 detects whether theseat 91 has a liquid spill, such as a water spill, and whether theliquid spill on the seat 91 is salt water or not. The distinction part74 may performs a similar determination, based on a detection result ofthe capacitance detecting part 73 and a predetermined threshold set inadvance.

The distinction part 74 switches between the occupant detection mode andthe spill detection mode based on a predetermined rule (e.g., at apredetermined interval). The distinction part 74 lights a water spilllamp when detecting the water spill, to stop the occupant detection orto perform the occupant detection based on a water spill consideredthreshold. The distinction part 74 instructs the switch part 76 toswitch the detection modes.

The op-amp 75 has the voltage application part 71 connected thereto onan input side, and has the sub-electrode 62 and the guard electrode 63connected thereto on an output side. In the occupant detection mode, theop-amp 75 applies, to sub-electrode 62 and the guard electrode 63, anelectric voltage that is same as the voltage applied to the mainelectrode 61. Therefore, in the occupant detection mode, the mainelectrode 61, the sub-electrode 62, and the guard electrode 63respectively have the same electric potential.

The switch part 76 switches its contact point according to aninstruction from the distinction part 74. The switch part 76 changes aconnection of the sub-electrode 62 based on an instruction from thedistinction part 74 between a contact point ‘a’ that is connected to anoutput terminal of the op-amp 75 and a contact point ‘b’ that isconnected to the vehicle grounding (GND) that is the reference electricpotential.

Specifically, the switch part 76 switches a connection of thesub-electrode 62 to (i) the contact point ‘a’ in the occupant detectionmode and (ii) to the contact point ‘b’ in the spill detection mode. Thesub-electrode 62 has the same electric potential as the main electrode61 in the occupant detection mode, and has the reference electricpotential in the spill detection mode to form an electric field togetherwith the main electrode 61.

The distinction part 74 detects whether the seat 91 has a liquid spillor not based on the capacitance between the main electrode 61 and thesub-electrode 62 in the spill detection mode.

By having the some electric potential as the main electrode 61, thefacing part 631 of the guard electrode 63 on the lower side of the mainelectrode 61 prevents a formation of the electric field that is formedby the main electrode 61 and the vehicle body 3. That is, a formation ofthe electric field by the main electrode 61 in a space other than abovethe seat 91 or the seat surface 911 (i.e., under the main electrode 61)is prevented in such manner.

Further, by having the same electric potential as the main electrode 61on both sides thereof in the H-axis, the sub-guard part 632 prevents aformation of an electric field by a peripheral portion of the mainelectrode 61 with the vehicle body 3. That is, a formation of theelectric field which does not pass through the seat surface 911 of theseat 91 is prevented in such manner.

According to the present embodiment, the sub-guard part 632 is disposedbetween the main electrode 61 and the sub-electrode 62, and such anarrangement of the sub-guard part 632 at a position close to the mainelectrode 61 prevents the unwanted capacitance coupling, therebyeffectively improving the detection accuracy for detecting an occupant.

By disposing the sub-guard part 632, the sub-electrode 62 is positionedat a moderately far-off position from the main electrode 61. In suchmanner, a difference of impedance values (i.e., a difference between avalue of a dry time when the seat 91 is dry and a value of a spill timewhen the seat 91 has a water spill) is increased, thereby improving thedetection accuracy of the water spill.

For instance, as shown in FIG. 20, the dry-wet difference of impedancevalues in the present embodiment is greater than the dry-wet differenceof impedance values in the conventional art that does not have thesub-guard part 632. That is, the configuration of the present embodimentenables the improvement of the detection accuracy for both of the spilldetection and the occupant detection without compromise, whilepreventing an influence from the sensor body 6 (i.e., while preventingthe unwanted capacitance coupling).

Although the present disclosure has been fully described in connectionwith the preferred embodiment thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbecome apparent to those skilled in the art.

For instance, the sub-guard part 632 and the facing part 631 may beconnected with each other in an inside of the occupant detection ECU 7.Further, as shown in FIG. 21, the detection voltage of the op-amp 75 maybe directly applied to the sub-guard electrode unit 632 without passingthrough the facing part 631.

Further, the first to third embodiments may be arbitrarily combined. Byproviding the switch part 76 for the first and second embodiments, thesub-electrode may be used as an electrode for the detection of theliquid spill.

Such changes and modifications are to be understood as being within thescope of the present disclosure as defined by the appended claims.

What is claimed is:
 1. A sensor body of a capacitance-type occupantdetection sensor for detecting an occupant seated on a seat of a vehiclebased on a capacitance value between a reference voltage and the sensorbody, the sensor body being disposed in the seat, the sensor bodycomprising: a main electrode having a detection voltage applied thereto;and a parallel electrode disposed in parallel with the main electrodewith a gap interposed therebetween, the parallel electrode having thedetection voltage applied thereto, wherein the main electrode and theparallel electrode each have a base material, a first electrode memberdisposed on the base material, and a second electrode member disposed onthe base material to cover the first electrode member, the secondelectrode member has an electric conductivity lower than the firstelectrode member, and the first electrode member is disposed on alateral perimeter of the second electrode member to surround a center ofthe second electrode member.
 2. A sensor body of a capacitance-typeoccupant detection sensor for detecting an occupant seated on a seat ofa vehicle based on a capacitance value between a reference voltage andthe sensor body, the sensor body being disposed in the seat, the sensorbody comprising: a main electrode having a detection voltage appliedthereto, the main electrode having a loop portion and a non-loopportion, the loop portion having a terminating end connected to the mainelectrode, and the non-loop portion extending from the loop portion; aparallel electrode disposed in parallel with the main electrode with agap interposed therebetween, the parallel electrode having the detectionvoltage applied thereto, wherein the parallel electrode is disposedalong a first lateral side of the loop portion, and has a starting endand a terminating end positioned on both sides of the non-loop portion;and a guard electrode arranged to face the main electrode and having asame voltage applied thereto as the detection voltage, the guardelectrode having a facing part and a protrusion part, wherein the facingpart faces the main electrode and the protrusion part extends from thefacing part in a direction away from the parallel electrode, such thatthe protrusion part extends towards a second lateral side of the loopportion, which is opposite of the first lateral side of the loopportion.
 3. A capacitance-type occupant detection sensor comprising: asensor body disposed in a seat of a vehicle and including: a mainelectrode having a detection voltage applied thereto, a parallelelectrode disposed in parallel with the main electrode with a gapinterposed therebetween, the parallel electrode having the detectionvoltage applied thereto, and a guard electrode having a facing part anda sub-guard part, the facing part arranged to face the main electrode,the sub-guard part disposed between the main electrode and the parallelelectrode, and the facing part and the sub-guard part having a samevoltage applied thereto as the detection voltage; and a detection partdetecting an occupant on the seat based on a capacitance value betweenthe main electrode and a reference electrode, wherein the detection partdetects a liquid spill on the seat based on a capacitance between themain electrode and the parallel electrode when a predetermined voltageis applied to the parallel electrode.